1. Field of the Invention
The invention relates to cylinders having a shuttle piston, i.e. rodless axially moving piston, having a power transmission element projecting from said piston through a longitudinal slot in the wall of the cylinder barrel, and a flexible seal band which serves to seal the longitudinal slot and is guided under and through the power transmission element.
2. Description of the Prior Art
The German Pat. No. 2,162,572 discloses a cylinder with a shuttle piston of this sort. This cylinder has a seal band made of magnetizable steel. Along the cylinder a row of magnets is placed to retain the seal band in a groove in the wall of the longitudinal slot and keep the seal band from sagging into the space within the cylinder. However, the use of magnets makes this known design complex and the design does not perform satisfactorily because the longitudinal slot is not so effectively shut off from the outside that it is not possible for dirt to find its way into it.
The German Pat. No. 3,124,878 discloses a shuttle piston cylinder, that uses an inner and an outer seal band both made of elastomeric material. The inner band has a longitudinal rib thereon with wedge faces and the outer band has a longitudinal groove also with wedge faces that are to cooperate with those of the rib. In step with motion of the piston in the cylinder, the rib is continuously guided out of the groove to one side of the piston and on the other side thereof it is moved back into the groove, the wedge faces of the rib loosely interlocking with those of the groove. This design of the seal band does, it is true, make possible an external sealing action (viz. To keep out material from the outside) as well and the inner seal band is kept from sagging into the space inside the cylinder, but however this is only possible with two seal bands, that have to be continuously engaged and disengaged with each other. Since the seal bands are made of an elastomeric synthetic material, the strength and stability of the unit are relatively poor.